[PATCH AUTOSEL 6.11 079/244] net: napi: Prevent overflow of napi_defer_hard_irqs

Sasha Levin
2024-09-25T11:39:51Z

From: Joe Damato <jdamato@fastly.com>

[ Upstream commit 08062af0a52107a243f7608fd972edb54ca5b7f8 ]

In commit 6f8b12d661d0 ("net: napi: add hard irqs deferral feature")
napi_defer_irqs was added to net_device and napi_defer_irqs_count was
added to napi_struct, both as type int.

This value never goes below zero, so there is not reason for it to be a
signed int. Change the type for both from int to u32, and add an
overflow check to sysfs to limit the value to S32_MAX.

The limit of S32_MAX was chosen because the practical limit before this
patch was S32_MAX (anything larger was an overflow) and thus there are
no behavioral changes introduced. If the extra bit is needed in the
future, the limit can be raised.

Before this patch:

$ sudo bash -c 'echo 2147483649 > /sys/class/net/eth4/napi_defer_hard_irqs'
$ cat /sys/class/net/eth4/napi_defer_hard_irqs
-2147483647

After this patch:

$ sudo bash -c 'echo 2147483649 > /sys/class/net/eth4/napi_defer_hard_irqs'
bash: line 0: echo: write error: Numerical result out of range

Similarly, /sys/class/net/XXXXX/tx_queue_len is defined as unsigned:

include/linux/netdevice.h: unsigned int tx_queue_len;

And has an overflow check:

dev_change_tx_queue_len(..., unsigned long new_len):

if (new_len != (unsigned int)new_len)
return -ERANGE;

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Joe Damato <jdamato@fastly.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20240904153431.307932-1-jdamato@fastly.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
Documentation/networking/net_cachelines/net_device.rst | 2 +-
include/linux/netdevice.h | 4 ++--
net/core/net-sysfs.c | 6 +++++-
3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/Documentation/networking/net_cachelines/net_device.rst b/Documentation/networking/net_cachelines/net_device.rst
index 70c4fb9d4e5ce..d68f37f5b1f82 100644
--- a/Documentation/networking/net_cachelines/net_device.rst
+++ b/Documentation/networking/net_cachelines/net_device.rst
@@ -98,7 +98,7 @@ unsigned_int num_rx_queues
unsigned_int real_num_rx_queues - read_mostly get_rps_cpu
struct_bpf_prog* xdp_prog - read_mostly netif_elide_gro()
unsigned_long gro_flush_timeout - read_mostly napi_complete_done
-int napi_defer_hard_irqs - read_mostly napi_complete_done
+u32 napi_defer_hard_irqs - read_mostly napi_complete_done
unsigned_int gro_max_size - read_mostly skb_gro_receive
unsigned_int gro_ipv4_max_size - read_mostly skb_gro_receive
rx_handler_func_t* rx_handler read_mostly - __netif_receive_skb_core
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 607009150b5fa..39eafd2e2368a 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -356,7 +356,7 @@ struct napi_struct {

unsigned long state;
int weight;
- int defer_hard_irqs_count;
+ u32 defer_hard_irqs_count;
unsigned long gro_bitmask;
int (*poll)(struct napi_struct *, int);
#ifdef CONFIG_NETPOLL
@@ -2091,7 +2091,7 @@ struct net_device {
unsigned int real_num_rx_queues;
struct netdev_rx_queue *_rx;
unsigned long gro_flush_timeout;
- int napi_defer_hard_irqs;
+ u32 napi_defer_hard_irqs;
unsigned int gro_max_size;
unsigned int gro_ipv4_max_size;
rx_handler_func_t __rcu *rx_handler;
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 291fdf4a328b3..93dd5d5436849 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -32,6 +32,7 @@
#ifdef CONFIG_SYSFS
static const char fmt_hex[] = "%#x\n";
static const char fmt_dec[] = "%d\n";
+static const char fmt_uint[] = "%u\n";
static const char fmt_ulong[] = "%lu\n";
static const char fmt_u64[] = "%llu\n";

@@ -425,6 +426,9 @@ NETDEVICE_SHOW_RW(gro_flush_timeout, fmt_ulong);

static int change_napi_defer_hard_irqs(struct net_device *dev, unsigned long val)
{
+ if (val > S32_MAX)
+ return -ERANGE;
+
WRITE_ONCE(dev->napi_defer_hard_irqs, val);
return 0;
}
@@ -438,7 +442,7 @@ static ssize_t napi_defer_hard_irqs_store(struct device *dev,

return netdev_store(dev, attr, buf, len, change_napi_defer_hard_irqs);
}
-NETDEVICE_SHOW_RW(napi_defer_hard_irqs, fmt_dec);
+NETDEVICE_SHOW_RW(napi_defer_hard_irqs, fmt_uint);

static ssize_t ifalias_store(struct device *dev, struct device_attribute *attr,
const char *buf, size_t len)
--
2.43.0